Face mask for deflecting respiratory aerosols generated by the wearer

ABSTRACT

A facemask to be worn in an enclosed space by a subject having or suspected of having a disease transmitted in exhaled aerosol particles is provided. The facemask comprises an air-permeable body having an outer surface facing away from the face of the subject, an inner surface facing toward the face, an upper edge cephalad, a lower edge caudad, and lateral edges at each side of the face such that the inner surface covers the subject&#39;s nose and mouth and is spaced apart therefrom. Moreover, at least a portion of the upper and lower edges is spaced apart from the face, but the lateral edges are not spaced apart. The upward and downward deflection of aerosol plumes exiting the facemask cooperates with airflow in the enclosed space to reduce exposure of occupants of the space to the subject&#39;s exhaled aerosol particles.

FIELD OF INVENTION

The present invention relates to a facemask adapted to provide a means of directing aerosol plumes expelled by a wearer of the facemask in a ventilated enclosure to flow upward toward the roof or ceiling of the enclosure or downward toward the floor of the enclosure, away from the mid-level space (“eye-level”) of the enclosure. The invention relates, further, to a method of reducing the likelihood that expelled aerosol will be inhaled by occupants of the enclosure.

BACKGROUND

Airborne diseases, transmitted in aerosol droplets when infected persons exhale, cough or sneeze, continue to challenge public health professionals and health care providers, particularly in the context of controlling outbreaks of airborne communicable diseases. Especially urgent is the need for a means of intervening effectively when a new, highly communicable, serious or life threatening disease breaks out in a population, particularly if the disease is resistant to treatment or difficult to treat with existing therapies. The social and economic advantages of living in urban environments only add to the urgency, inasmuch as one often realizes those very advantages by intermingling with others at high density in environments such as subways, workplaces, hospitals, schools, malls and restaurants. One such environment in particular the commercial aircraft tends to transform local outbreaks into global pandemics, as avian flu and severe acute respiratory syndrome (SARS) have recently shown. New sources for airborne pathogens have also been recognized. These include vectors such as livestock, in which pathogenic strains with the power to infect humans may emerge. It is also conceivable that advances in genetic engineering will produce intentionally engineered airborne pathogens for use as bio-terror weapons.

Disposable and non-disposable facemasks have been employed for many years in an effort to limit the transmission of airborne communicable diseases. Masks were first used in medical practice to prevent contamination and resulting infection of patients, particularly during surgery. In recent years, there has also been an increased awareness and concern for preventing contamination and infection of the public by airborne pathogens outside of medical environments. Among other measures, individuals who are exposed, or suspect they will be exposed, to infectious aerosols, have resorted to wearing one or another version of a facemask to protect them from the threat. Much current literature focuses on inhalational barrier protection (filtration) to be worn by healthcare workers (“HCW”) [8-11]. In non-healthcare settings, facemasks are also recommended for use by symptomatic persons when they are in public places to limit the risk of transmission to others in close contact with them [5, 12, 13]. However, the efficacy of this measure has not been quantified in terms of relative protection utilizing current National Institute of Occupational Safety and Health (NIOSH) workplace protection factors (WPF).

The standard protective facemask is a disposable, air-permeable paper or paper-like mask that falls generally into one of two categories: molded, cup-shaped masks and fold-flat masks. Molded cup-shaped masks (often referred to as “N95 masks”) offer the advantage of having a firmly constructed mask body that tends to contact the cheeks, chin and bridge of the nose but is spaced apart from the wearer's nose and mouth. They may be formed from one or more layers of air-permeable material. Examples of such masks are described in U.S. Pat. Nos. 4,536,440; 4,807,619; 4,850,347; 5,307,796 and 5,374,458.

Fold-flat masks are constructed to fold flat for storage and to open out to provide a cup-shaped air chamber or plenum over the mouth and nose of the wearer during use. These masks may also be formed from layers of material permeable to air. Examples of fold-flat masks are described in U.S. Pat. Nos. 5,322,061; 5,020,533; 4,920,960 and 4,600,002.

A recent report has suggested that the use of standard ear loop procedural (surgical) masks (i.e., “fold-flat” masks) may reduce transmission of influenza-like illness [1]. The Centers for Disease Control and Prevention (CDC) indeed recommends such masks for seasonal influenza, but recommends the N95, molded, cup-shaped mask for maximum protection of health care workers during outbreaks of diseases such as avian influenza, SARS and the H1N1 virus [2-5]. The recommendation of the fold-flat mask is based on the assumption that influenza is contracted via direct contact or by the transmission of large (>5 μm), airborne droplets [6], whereas bird flu, SARS and H1N1 are transmitted in smaller (<5 μm) aerosolized particles that would be better intercepted by the greater filtration capability of N95 respirators [7]. However, there is no firm understanding of the various potential transmission mechanisms of influenza [3, 4]. The current literature focuses on inhalational barrier protection (filtration) worn by healthcare workers (“HCW”) [8-11].

Facemasks qualify as “respirators” if they have a means of supplying breathing air to the wearer that is cleaner (at least presumably) than the air the wearer would breathe absent the respirator. The aforementioned air-permeable material that comprises typical disposable masks is thought to provide this capability by filtering and “scrubbing” air as it flows into the mask upon inhalation, such that contaminants are left behind in or on the mask material. Various means of preventing or reducing the intake of potentially contaminated air that “leaks in” around the filter element have been devised, including wires, stays, resilient materials and adhesives to urge the edges of the mask against the cheeks, chin and bridge of the nose. So that exhalation does not compromise the performance of these anti-leak elements, a variety of exhaust valves have been conceived to limit the build-up of positive pressure within the mask. More complex respirators dispense with filtration partially or entirely by providing a source of “pure” air from a tank or other reservoir. Some respirators rely, at least in part, on “re-breathing” exhaled air by removing carbon dioxide from it.

Masks for use by a source of contamination rely on filtration-type devices that presumably capture exhaled or expelled contaminants such as pathogen-laden aerosol particles before they can reach ambient air. Again, measures may be taken to discourage leaks of exhaled air at the upper, lower and lateral edges of the mask, with the intention of forcing as much of the exhaled air as possible through the mask's filtering elements. In general, the filtering elements also provide the major pathway for taking air in, although means for reducing resistance to the influx of inhalation air have been devised.

As a practical matter, most facemasks, whether fold-flat (originally used to block exhaled contaminants) or molded (originally designed to block inhaled contaminants), are “dual-use” devices. That is, the wearer may intend to protect himself from being a recipient of airborne infectious diseases, or he may intend to protect others by relying on the mask to limit the “broadcasting” of airborne pathogens when he exhales, coughs or sneezes. In either case, he wears the same or a similar mask.

The use of facemasks in public areas such as hospitals, mass transit systems and other places of congregation as well as poultry processing facilities is sometimes mandated by health authorities to limit the spread of outbreaks of potentially serious diseases capable of airborne transmission. In addition to ordering the wearing of facemasks, health authorities have historically taken additional precautions by ordering the quarantine or exclusion of persons considered at high risk of spreading or contracting an infection. Faced with the influenza pandemic of 1918, for example, the state of New York issued an order prohibiting congregation of citizens in public areas. During the SARS outbreak in China that occurred between November, 2002 and July, 2003, the Chinese government quarantined residents of certain areas to prevent the potential spread of the disease. In 2003, Toronto health authorities mandated a procedure in which arriving airline passengers were individually screened for potential SARS infection by means of an electronic thermometer placed in the ear of each passenger upon arrival. Also in 2003, thermal imaging scans were instituted to screen passengers at Chiangi airport in Singapore. Such measures may have been more widely applied had it not been for the laborious process of testing persons one-by-one as well as the associated inconvenience and delays imposed upon the tested subjects.

Current guidelines and recommendations of the Centers for Disease Control (“CDC”) recommend the use of facemasks to control influenza when suboptimal immunization of the public could increase the frequency of influenza infection. Human influenza is thought to be transmitted from person to person primarily via virus-laden droplets that are generated when infected persons cough or sneeze. These sometimes relatively large droplets (>5μ in diameter) can be directly deposited onto the mucosal surfaces of the upper respiratory tract of susceptible persons who are near (viz., within 3 feet) of the droplet source. Transmission also may occur through direct and indirect contact with infectious respiratory secretions or infectious expiratory droplets or airborne droplet nuclei. Without regard to their size, the CDC refers to all such droplets as “respirable.”

A combination of infection control strategies is recommended by public health authorities to decrease transmission of influenza in health-care settings. These include placing influenza patients in private rooms when possible, and having health-care personnel wear masks for close patient contact (i.e., within 3 feet) and gowns and gloves if contact with expiratory droplets is likely. The use of surgical (or “procedure”) masks by infectious patients is generally thought to help contain their expiratory droplets and limit exposure to others. Likewise, when a patient is not wearing a mask, as when in an isolation room, having health-care personnel wear masks for close contact with the patient may prevent nose and mouth contact with respiratory droplets. In the United States, disposable surgical and procedure masks have been used widely in healthcare settings to prevent exposure to respiratory infections, but they have not been used commonly in community settings (e.g. schools, businesses, and public gatherings).

A surprising finding by the Applicant has shown that the aforementioned recommended practices are not as effective as heretofore assumed. As the Examples herein clearly show, filtering ambient air by inhaling the air through an air-permeable surgical mask (“infiltration”) is an ineffective means of removing aerosols from the air. Exfiltration is also relatively ineffective in removing aerosols from air as they are being exhaled. That is, even when a source is wearing a facemask having a filter element, aerosol particles tend to escape. On the other hand, devices that entirely capture exhaled air or that provide a source of purified breathing air (such as a valve-regulated air tank) are not suitably convenient or inexpensive, particularly for public health purposes.

All patents and published patent applications referenced herein are hereby incorporated by reference in their entirety.

SUMMARY OF THE INVENTION

In its various embodiments, the invention provides an air-permeable facemask adapted to deflect a flow of aerosolized particles in air exhaled or expelled from the nose or mouth of a subject who is a source of contaminated or putatively contaminated aerosol particles. In preferred embodiments, expelled air, with aerosol particles dispersed therein, is deflected upward or downward out of the mask, and not laterally. In enclosed, ventilated spaces, the embodiments have the advantage of reducing the accumulation of exhaled aerosol particles at mid-level in the enclosed space (i.e., at “eye level”) where other occupants can readily inhale them or adsorb them on their skin or clothing. In some embodiments, the upwardly deflected exhalants form plumes that are advantageously diluted in ambient air overhead. In some embodiments, the downwardly deflected exhalants form plumes that are advantageously adsorbed on the clothing of the source, or diluted in air circulating near the floor of the enclosed space. Preferably, in either case, ventilation in the enclosure removes diluent air and replaces it with fresh (or “make-up”) air.

In one embodiment, the invention provides a facemask configured to be worn by a subject, said subject having a face comprising a medially disposed nose extending cephalad to a nose-bridge, a mouth disposed inferiorly to said nose, and a chin disposed inferiorly to said mouth, cheeks laterally, eyes cephalad of said cheeks and a forehead cephalad of said eyes, wherein said subject exhales or expels aerosol particles from said nose or mouth, and wherein said facemask comprises an air-permeable body having, in use, an outer surface facing away from said face, an inner surface facing toward said face, an upper edge cephalad, a lower edge caudad, and lateral edges at each side of said face such that:

-   -   a) said inner surface covers said nose and mouth and is spaced         apart therefrom;     -   b) at least a portion of said upper edge is spaced apart from         said face;     -   c) at least a portion of said lower edge is spaced apart from         said face, and     -   d) said lateral edges are not spaced apart from said face.

In one embodiment, at least a portion of said upper edge of said facemask is spaced apart from said nose-bridge and said forehead, and at least a portion of said lower edge is spaced apart from said chin. In another embodiment, the facemask further comprises an eye-level region spaced apart from, and covering, at least a portion of said eyes. In still another embodiment, the facemask further comprises a forehead-level region spaced apart from, and covering, at least a portion of said forehead.

In one embodiment, the inner surface of said facemask comprises lateral regions spaced apart from said cheeks.

In one embodiment, said upper and lower edges of said facemask are spaced apart from said face medially.

In a preferred embodiment, said lateral edges of said facemask contact said cheeks. In a more preferred embodiment, said lateral edges are urged into contact with said cheeks by an urging means.

In one embodiment, said facemask is configured such that said volume of air expelled from said nose or mouth comprises a first portion deflected cephalad to create a first deflected volume, and a second portion deflected caudad to create a second deflected volume. In a preferred embodiment, at least a portion of said first or second deflected volume flows out of said facemask to create a deflected aerosol plume.

In one embodiment, said volume of air expelled from said nose or mouth comprises a third portion deflected laterally toward said lateral edges of said mask body to create a third deflected volume. In one embodiment, said first and second deflected volumes, in combination, are greater than said third deflected volume.

In one embodiment, said inner surface of said facemask is spaced apart from said face to create a plenum. In one embodiment, said plenum comprises a first portion disposed over said nose and said mouth, and a second portion disposed lateral to said nose and mouth bilaterally. In one embodiment, said first portion of said plenum is sized relative to said second portion such that said first portion is of a greater size than said second portion. In a preferred embodiment, said first portion of said plenum extends cephalad to a first opening at said upper edge of said facemask body, wherein said face and said upper edge define said first opening. In one embodiment, said first portion of said plenum extends caudad to a second opening at said lower edge of said facemask body, wherein said face and said lower edge define said second opening.

In one embodiment, said body of said facemask comprises a rigid material. In another embodiment, said body comprises a flexible material. In one embodiment, said flexible material is elastic.

In one embodiment, said body of said facemask comprises a first portion comprising an air-impermeable material and a second portion comprising an air-permeable material.

In one embodiment, said plenum of said facemask cannot sustain within it over an entire breathing cycle a positive pressure relative to ambient air outside said plenum.

In another embodiment, the invention comprises a system comprising:

-   -   a) said facemask, and     -   b) an enclosure comprising a floor, a ceiling and a wall         therebetween, wherein said floor, ceiling and wall define an         enclosed space, and wherein said enclosed space contains an         ambient, breathable gas.

In one embodiment, said enclosed space comprises an overhead space, a mid-level space disposed below said overhead space and a lower-level space disposed below said mid-level space, wherein said overhead and mid-level spaces are contiguous and in fluid communication and wherein said mid-level and lower-level spaces are contiguous and in fluid communication.

In a preferred embodiment, said enclosure is ventilated. In one embodiment, said ceiling, wall or floor is fenestrated. In one embodiment, said enclosure is ventilated at a rate of at least five enclosure volume exchanges per hour. In one embodiment, said enclosure is ventilated by an air handler.

In one embodiment, the invention provides a method of positioning a facemask on a human subject, comprising a) providing a facemask comprising an air-permeable body having an outer surface, an inner surface, an upper edge, a lower edge and lateral edges; and b) positioning said facemask on the face of said human subject such that said outer surface faces away from the face of said subject, said inner surface faces toward said face, said upper edge is positioned cephalad, said lower edge is positioned caudad, and said lateral edges contact each side of said face such that:

-   -   i) said inner surface covers the human subject's nose and mouth         and is spaced apart therefrom so as to create a plenum defined         by said upper, lower and lateral edges and having only first and         second openings;     -   ii) at least a portion of said upper edge is spaced apart from         said face so as to define said first opening;     -   iii) at least a portion of said lower edge is spaced apart from         said face so as to define said second opening, and     -   iv) said lateral edges are not spaced apart from said face and         are in contact with the cheeks of said face.

In another embodiment, the invention provides a method of reducing an accumulation of aerosol particles in at least a mid-level space of a ventilated enclosure consequent to an aerosol plume created by a subject in said enclosure, the method comprising the steps of:

-   -   a) providing         -   i) said subject;         -   ii) said ventilated enclosure;         -   iii) said facemask, and         -   iv) a pre-determined standard accumulation of said airborne             aerosol particles in said mid-level space;     -   b) positioning said facemask on said face over said nose and         mouth to create a positioned mask, and     -   c) causing said subject to create an aerosol plume, such that         said accumulation is less than said standard accumulation.

In one embodiment of said method, said subject has, or is suspected of having, a disease spread by airborne aerosol particles.

DEFINITIONS

To facilitate understanding of the descriptions herein of embodiments of the invention, a number of terms (set off in quotation marks in this Definitions section) are defined below. Terms defined herein (unless otherwise specified) have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. As used in this specification and its appended claims, terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration, unless the context dictates otherwise. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

The phrase “chosen from A, B, and C” as used herein, means selecting one or more of A, B, C.

As used herein, absent an express indication to the contrary, the term “or” when used in the expression “A or B,” where A and B may refer to a composition, object, disease, product, etc., means one or the other (“exclusive OR”), or both (“inclusive OR”). As used herein, the term “comprising” when placed before the recitation of steps in a method means that the method encompasses one or more steps that are additional to those expressly recited, and that the additional one or more steps may be performed before, between, and/or after the recited steps. For example, a method comprising steps a, b, and c encompasses a method of steps a, b, x, and c, a method of steps a, b, c, and x, as well as a method of steps x, a, b, and c. Furthermore, the term “comprising” when placed before the recitation of steps in a method does not (although it may) require sequential performance of the listed steps, unless the context dictates otherwise. For example, a method comprising steps a, b, and c encompasses, for example, a method of performing steps in the order of steps a, c, and b, the order of steps c, b, and a, and the order of steps c, a, and b, etc.

Unless otherwise indicated, all numbers expressing quantities in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained in a particular embodiment of the present invention. At the very least, and without limiting the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Any numerical value, however, inherently contains deviations that necessarily result from the errors found in the numerical value's testing measurements.

The term “not” when preceding, and made in reference to, any particularly named entity or phenomenon means that only the particularly named entity or phenomenon is excluded.

The term “altering” and grammatical equivalents as used herein in reference to any entity and/or phenomenon refers to an increase and/or decrease in the quantity of the entity in a given space and/or the intensity, force, energy or power of the phenomenon, regardless of whether determined objectively, and/or subjectively.

The terms “increase,” “elevate,” “raise,” and grammatical equivalents when used in reference to the quantity of an entity and/or the intensity, force, energy or power of a phenomenon in a first sample relative to a second sample, mean that the quantity of the entity and/or the intensity, force, energy or power of the phenomenon in the first sample is higher than in the second sample by any amount that is statistically significant using any art-accepted statistical method of analysis. In one embodiment, the increase may be determined subjectively, for example when a patient refers to their subjective perception of disease symptoms, such as pain, clarity of vision, etc. In another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 10% greater than the quantity of the same substance and/or phenomenon in a second sample. In another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 25% greater than the quantity of the same substance and/or phenomenon in a second sample. In yet another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 50% greater than the quantity of the same substance and/or phenomenon in a second sample. In a further embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 75% greater than the quantity of the same substance and/or phenomenon in a second sample. In yet another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 90% greater than the quantity of the same substance and/or phenomenon in a second sample. Alternatively, a difference may be expressed as an “n-fold” difference.

The terms “reduce,” “inhibit,” “diminish,” “suppress,” “decrease,” and grammatical equivalents when used in reference to the quantity of an entity and/or the intensity, force, energy or power of a phenomenon in a first sample relative to a second sample, mean that the quantity of an entity and/or the intensity, force, energy or power of a phenomenon in the first sample is lower than in the second sample by any amount that is statistically significant using any art-accepted statistical method of analysis. In one embodiment, the reduction may be determined subjectively, for example when a patient refers to their subjective perception of disease symptoms, such as pain, weakness, etc. In another embodiment, the quantity of quantity of an entity and/or the intensity, force, energy or power of a phenomenon the first sample is at least 10% lower than the quantity of the same substance and/or phenomenon in a second sample. In another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 25% lower than the quantity of the same substance and/or phenomenon in a second sample. In yet another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 50% lower than the quantity of the same substance and/or phenomenon in a second sample. In a further embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 75% lower than the quantity of the same substance and/or phenomenon in a second sample. In yet another embodiment, the quantity of the substance and/or phenomenon in the first sample is at least 90% lower than the quantity of the same substance and/or phenomenon in a second sample. Alternatively, a difference may be expressed as an “n-fold” difference.

A “standard” quantity of an entity and/or a “standard” intensity, force, energy or power of a phenomenon relates to that quantity, intensity etc. found in a control or “null” experiment conducted when all controllable variables are held constant or have known values. A “standard accumulation” of airborne aerosol particles, for example, may be the number of aerosol particles captured on a filter placed three feet from a source of an aerosol plume generated by a single cycle of a source of the plume wherein said plume is directed at said filter under a pre-determined, reproducible set of conditions.

The term “contact,” when used herein to refer to physical contact between two bodies or surfaces, encompasses passive contact and, especially, contact reinforced or maintained by an applied force or pressure or other menas of urging one of the bodies or surfaces into contact with the other.

As used herein, the term “deflect,” and variants thereof, generally refers to a change in the direction of an inertially moving object consequent to a collision of that object with a surface from which the object rebounds. Where the context so admits, however, the twin may be used to describe a displacement of a structural element (e.g., twisting, bending) under a load. It is not intended that the size of the moving object be limiting, although microscopic objects such as gas molecules and particles suspended in air find frequent reference herein. Neither is it intended that the moving object be isolated in any way. The term may refer to a deflection of a stream or train of objects flowing in bulk. Moreover, the objects or particles in the stream need not be disposed in a uniform or ordered configuration. Microscopic liquid droplets suspended in and moving through air (sometimes referred to herein as a “plume”) are a relevant but non-limiting example. As the term is used herein, the “interception” of an inertially moving object by a surface may result in its deflection, “adsorption,” or “absorption.” Interception alters the vector that describes the speed and direction of the moving object. The intercepted object may adhere to the surface (“adsorption”), with or without wetting the surface, or it may bounce off the surface (“deflection”). “Adsorbed” substances may ultimately be “absorbed.” That is, they may dissolve or disperse in other substances that comprise the material.

As used herein, the term “flow” refers generally to the movement of a gas or liquid and, more specifically, to the rate of such movement, measured either as a volume or a mass of the fluid passing a given area in a unit of time.

In general, an “aerosol” is a suspension of dry or liquid microscopic particles dispersed in a gas. Herein, the term refers particularly to liquid droplets that are suspended in the breath of subjects or that migrate therefrom into ambient air in an enclosure occupied by such subjects. It is to be understood that water vapor in the breath is not an aerosol. Subjects make or “generate” aerosol particles in many ways, including but not limited to condensation of water vapor into microscopic droplets.

The term “particle” refers herein especially to colloidal particles, defined as particles mixed with at least one other substance or material in a single phase, wherein no individual particle is visible. Liquid droplets suspended in air are exemplary. In the context of the instant application, the term “air” encompasses air as it is found in the earth's atmosphere, conditioned air, air enriched with oxygen, carbon dioxide and other gases compatible with life, and, without limitation, pollutants, odorants, and antimicrobial agents. The term “ambient” as used herein refers to properties that pervade an environment. The composition (or temperature, etc.) of “ambient air” in an environment is approximately invariant from place to place in that environment.

The terms for facial features (face, nose, mouth, chin, cheeks, eyes, forehead) are used herein according to common usage. It will be understood that regions of the face may be identified herein by these features. For example the region of the face at “eye-level” extends approximately from eyebrows to upper cheeks. The bridge of the nose is a medial structure but is at eye-level. The region above the eyebrows to the (non-receded) hair line, encompasses the forehead. Facial features are somewhat variable even within an individual. For example, opening the mouth redefines the “layout” of facial features to some extent. One can “puff” the cheeks or raise the eyebrows. It will be understood that a facial region defined herein by a facial feature is intended to take such variability into account. For example, a facemask element that “covers the mouth” refers to an element that is capable of covering an open mouth or a closed mouth, unless otherwise specifically noted.

As used herein in reference to a patient or subject, a “source” refers to a subject who generates and expels aerosol in the course of breathing (tidally or otherwise), coughing, sneezing, etc. A “recipient” or “receiver” refers to a subject who inhales or receives such aerosol on the surface of his body.

“Contamination,” and variants thereof, refers generally to an impurity or unwanted substance mixed with or contacting another material. Herein, contamination refers especially to pathogenic bacteria, viruses, and the like, but it is not intended that the term be limited thereto. Any substance or material for which embodiments of the invention reduce recipient exposure is a contaminant.

As used herein, the term “caudad,” when used in conjunction with the face of a wearer of a mask according to embodiments of the invention, is interchangeable with the term “downward” and means “toward the feet” when the wearer is standing, walking or sitting. “Cephalad” is interchangeable with the term “upward” and means “in a direction opposite to caudad” when a wearer of the mask is standing, walking or sitting.

The term “enclosure” is used herein interchangeably with “enclosed space,” “indoors” and the like. It is not intended that an enclosure be air-tight or sealed off from a larger space. Any enclosure having a roof or ceiling, a floor and wall elements therebetween that substantially delineate the enclosed space is within the scope of the term. Non-limiting examples of an enclosure include tents, residential dwellings, a room within a dwelling, an office or conference room in a building, a passenger car in a train or subway, etc. As used herein, the term “ventilation” relates to the movement of air into an enclosure from a source outside the enclosure. It is not intended that the term be limited to any particular means of moving or transferring the air or any particular rate of movement. Any such transfer that meets the ventilation needs of any embodiment in achieving an objective of an embodiment of the invention is within the scope of the invention. Thus, the enclosure may be ventilated naturally by means of an open window or door (a “fenestration”), for example, or by forcing air to move by means of fans (intake fans, exhaust fans, air handling systems, etc.). The ventilation system may be “closed” such that a portion of the moving air is recycled and another portion is exhausted from the enclosure to be replaced by “make-up” air obtained from outside the enclosure. A combination of air-moving means may be employed, and the combination may vary over time.

The term “accumulation,” and variants thereof, is used herein to refer to any increase over time of a quantity, amount, volume or mass of a substance on a unit of surface or within a space. The unit of surface or space on or in which the accumulation takes place is said to have been “exposed” to that quantity, amount, volume or mass of the substance.

A “workplace protection factor” (“WPF”) is used herein especially in relation to facemasks used to prevent or help prevent subjects in a workplace or other enclosure from inhaling aerosol particles expelled by a subject also occupying that enclosure. WPF equals the ratio of exposure without a mask to exposure with a mask. Any means of reproducibly measuring such exposures is within the scope of the invention. One means is to use a filter adapted to capture and count all of the aerosol particles in air passing therethrough. Such filters, one of which is described herein, are well-known in the art.

As used herein, “inhalation” (or “inspiration”), and its variants, refers to the movement of an amount of air from a region outside the body of a subject into a space within the subject. The term generally refers to a subject's taking of air from outside the body into the alveoli of the lung, but can encompass “sniffing,” “gulping,” etc. Air so moved may be referred to as an “inhalant.” “Exhalation” (or “expiration”), and its variants, refer to movement of an amount of air within an airway or lung of a subject to a space outside the body. Air so moved may be referred to as an “exhalant.” It is not intended that the term be limited by the rate at which such air moves or the force of the exhalation. Thus, The expulsion of air associated with coughing, sneezing, eructation, speaking, singing or whistling, for example, is an exhalation herein.

To “dilute” a substance means to reduce the concentration of the substance in a phase (a “diluent”) in which the substance is dissolved, suspended or dispersed.

As used herein, the term “wear” and its variants (e.g., “wearer”), especially in relation to facemasks, refers to the use of a facemask by a subject for the purposes described herein. It will be understood that “wear” or “wearing” is not intended to connote only protection of the wearer. In some embodiments, the wearer uses the facemask to protect others.

An “urging means” as used herein relates to any means of initiating or maintaining a contact between two elements. A non-limiting but pertinent example is an elastic band or ribbon secured to the lateral edges of a facemask in such a manner that stretching the band around the back or the crown of the head creates a tension that causes the lateral edges of the facemask to firmly contact the lateral aspects of the cheeks. Alternatively, and without intending any limitation, an adhesive or other sealant might be used to maintain such contact.

The term “region” refers to an area or a space distinguishable by landmarks or boundaries from other regions of that area or space. Relevant landmarks and boundaries may be anatomical, geometric, or otherwise as long as they provide a frame of reference that is reproducible for purposes of describing embodiments of the invention. For example, the face extends “laterally” from the corners of the mouth to the ears and comprises the cheeks. The “medial” region of the face comprises the nose, mouth and chin. The “positioning” of facemasks referred to herein is described in the context of these anatomical features.

An enclosure may have an “overhead region,” or “overhead space,” defined as a space extending downward from the roof or ceiling of the enclosure to a level just above the heads of occupants of the enclosure, a “lower-level region” or “lower-level space” extending upward from the floor of the enclosure to a level at the waists of the occupants, and a “mid-level region” or “mid-level space” therebetween.

As used herein, the term “plenum” refers to a chamber or enclosure that may contain a quantity of a gas or other fluid at a positive pressure relative to pressure outside the chanber. The term, as used herein, need not connote stasis. That is, the fluid in a plenum may flow in or through the plenum and the pressure in the plenum may range from negative to positive.

The term “material” is to be construed broadly herein to refer to physical matter, irrespective of its properties.

The term “rigid,” as used herein, refers to any material that is stiff in the sense that it resists distortion (by twisting, bending, stretching, or compression). The term is intended to encompass both “elastic” and “inelastic” materials. An applied force may distort an elastic material, but when the applied force is removed, the material tends to return to its original shape. An inelastic material tends not to return to its original shape. A “flexible” material may also be either elastic or inelastic, but it is less resistant to distortion than a rigid material.

Although an “air-permeable” material, as used herein, may encompass materials that permit air to flow through them only under pressures substantially greater than atmospheric, the term refers more particularly herein to materials through which a subject can inhale comfortably when the material is covering the subject's nose and mouth. It will be understood that a material need not be in contact with the nose or mouth to “cover” the nose or mouth, but may be spaced apart therefrom. An “air-impermeable” material interferes with the flow of air through the material. As used herein, the term is not intended to convey “absolute” impermeability. Where an embodiment requires impermeability, its extent is sufficient if it achieves the objective of the embodiment. An “air-permeable” material, similarly, is sufficiently permeable if it achieves an objective served by permeability. The terms “air-permeable” and “aerosol permeable” (or impermeable) are used interchangeably herein unless the context dictates otherwise

A “breathing cycle,” as used herein, means the period of time required for a subject, beginning at the moment he has completed expelling a first volume of air from an airway, to take in a next succeeding volume of air into an airway and expel that volume out of the airway and ending at the moment he begins to take in a next succeeding volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Model of Source/Receiver/Environment interaction. Parameters that can be set or measured are shown.

FIG. 2. Schematic representation of experimental set-up. Breathing pattern of both Source and Receiver; tidal volume 500, rate 15, and duty cycle 0.5. Environmental flow in chamber was regulated via opening between hood and chamber. Cascade impactor measured particle distribution of aerosol inhaled by Receiver. Exposure defined by radioactivity captured on Exposure filter in Receiver.

FIG. 3. Experimental setup for Source aerosol measurements.

FIG. 4. Particle Distributions and Mass Median Aerodynamic Diameters for all stages of the cascade impactor. Mean+/−CI for each stage are plotted as log particle size (μm) vs. probability.

(S=Source; R=Receiver; MMAD=Mass Median Aerodynamic Diameter; MaxEx=Maximum Exposure; LSM=Loosely fit Surgical Mask; TSM=Tightly fit Surgical Mask) ∘Source MMAD=1.046 μm; 0 (S-None, R-None) MMAD=0.633 μm; □(S-LSM, R-None) MMAD=0.483 μm; ▴(S-TSM, R-None) MMAD=0.461 μm; ▪(S-N95, R-None) MMAD=0.470 μm

FIG. 5. Side-view of head showing plenum in fluid communication with upper and lower openings of mask body.

FIG. 6. Front view of head showing upwardly and downwardly deflected aerosol plumes.

FIG. 7. Photograph in side view showing aerosol plume expelled without facemask.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a facemask for reducing the likelihood that occupants in an enclosed space will inhale or be exposed to aerosol particles expelled by individuals when they exhale, cough or sneeze in that enclosure. The facemask is not intended to rely simply on trapping aerosol particles as the individual emits them from nose and mouth. The mask is not intended to rely on filtering, “scrubbing” or otherwise sterilizing the expelled air or substantially reducing the number of aerosol particles that reach ambient air overall. In preferred embodiments, the invention provides a facemask adapted to direct the aerosol plumes expelled by a wearer of the mask to flow upward toward the roof or ceiling of the enclosure and downward toward the floor of the enclosure, and not into the mid-level space (“eye-level”) of the enclosure. In this way, exhaled or expelled plumes are advantageously diluted in ambient air overhead, and then removed in air being vented from the space. In some embodiments, exhaled plumes are advantageously directed downward to be adsorbed on the clothing of the source, or diluted in air circulating near the floor of the enclosed space. Thus, in another aspect, the invention provides a method of reducing the likelihood that expelled aerosol will be inhaled by occupants of the enclosure.

The notion that the incorporation of air-filtering materials into facemasks, especially in combination with means for reducing or eliminating “leaks” at the upper, lower and lateral edges of the masks has inspired the creation of countless facemask designs. U.S. Pat. Nos. 4,616,647, 4,856,509, 4,945,907, 5,357,947, 7,047,139 are representative examples particularly relevant to disposable articles. In such cases, a “vent” through which a gas or aerosol can flow freely is not generally characterized as a vent but as a leak that tends to compromise filtration and is to be combated with seals, stays, ties, etc. Masks intentionally adapted for the purpose of venting are generally configured for delivering gases to subjects under pressure (anesthetics, oxygen for resuscitation, CPAP devices to provide continuous positive airway pressure, etc.), not to facilitate the removal of gases produced by the subjects.

To encourage exhaled or expelled aerosols to travel upward into the large volume of ambient air located above eye-level in an enclosed space, it is advantageous in preferred embodiments to keep at least a medial portion of the upper edge of the facemask spaced apart from facial surfaces. In preferred embodiments, therefore, although the mask may be a rigid material formed in a mold, for example, the upper edge thereof preferably does not contact the bridge or sides of the nose, or regions of the cheeks in the proximity of the nose. Prior art devices, by contrast, are variously adapted to ensure such contact. U.S. Pat. Nos. 4,037,593, 5,357,947 and 5,699,792 are exemplary.

To ensure that there will be no such contact in embodiments of the present invention, elements extending from the inner surface of the mask to contact the surface of the face are contemplated. In one embodiment, they act as spacers to stabilize the opening formed by the upper edge of the body of the mask, but it is not intended that such spacers materially interfere with the bulk flow of gases through the opening. It is to be understood that such spacers are contemplated solely as an example, not by way of limitation. In another embodiment, the body of the mask may comprise a rigid material, molded or shaped to define and preserve a space between the inner surface of the mask body and the face except at the lateral edges of the mask body. At the lateral edges, the molding preserves a shape that conforms to the contour of the cheeks and lower jaw such that the mask, in use, contacts facial surfaces. Flexible elastic elements in and near the lateral edges may be included to ensure that such contact is maintained when the contour changes or when pressure in the space between the inner surface of the mask's body and the face changes. It may be advantageous to employ stays or adhesives to keep the lateral edges in contact with the face. In various embodiments, the mask may be held in place over the face with ties or elastic bands that extend behind the head, or ear-loops or other means known in the art. It is contemplated that these means for holding the mask in place will cooperate with the aforementioned stays, elastic elements and adhesives to further encourage contact between the lateral edges of the mask body and the face.

Similarly, it is advantageous to leave the lower edge of the body of the mask spaced apart from facial surfaces in the proximity of the chin. Again, elements extending from the inner surface of the mask to contact the surface of the face are contemplated as spacers. And again, it is not intended that such spacers materially interfere with the bulk flow of gases through the opening formed by the surface of the face and the lower edge of the body of the mask. It will be understood that alternatives to spacers are also contemplated, including molding the mask with a rigid material that preserves the spacing. The lower edge of the mask preferably extends below the lower extent of the wearer's open mouth and may be configured to permit unobstructed articulation of the lower jaw.

It will be understood that masks in accordance with the invention need not be constructed of rigid materials, either in whole or in part. Acceptable materials include flexible materials such as paper and other non-woven materials, fabric, and resilient materials, provided only that they a) can be suitably spaced apart from the surface of the face medially when the mask is in use, b) resist deterioration from moisture, c) are sufficiently permeable to air to permit wearers of the mask to breathe comfortably, and d) are generally suitable to be worn by humans externally on the face.

An exemplary but non-limiting method of forming a mask according to the invention comprises providing at least one layer of fibrous material that can be molded to the desired shape with the use of heat and that retains its shape when cooled. Shape retention is typically achieved by causing the fibers to bond to each other at points of contact between them, for example, by fusion or welding. Any suitable material known for making a shape-retaining layer of a direct-molded respiratory mask may be used to form the mask shell, including, for example, a mixture of synthetic staple fiber, preferably crimped, and bicomponent staple fiber. Bicomponent fiber is a fiber that includes two or more distinct regions of fibrous material, typically distinct regions of polymeric materials. Typical bicomponent fibers include a binder component and a structural component. The binder component allows the fibers of the shape-retaining shell to be bonded together at fiber intersection points when heated and cooled. During heating, the binder component flows into contact with adjacent fibers. The shape-retaining layer can be prepared from fiber mixtures that include staple fiber and bicomponent fiber in weight-percent ratios that may range, for example, from 0/100 to 75/25. Preferably, the material includes at least 50 weight-percent bicomponent fiber to create a greater number of intersection bonding points, which, in turn, increase the resilience and shape retention of the shell.

Suitable bicomponent fibers that may be used in the shaping layer include, for example, side-by-side configurations, concentric sheath-core configurations, and elliptical sheath-core configurations. One suitable bicomponent fiber is the polyester bicomponent fiber available, under the trade designation “KOSA T254” (12 denier, length 38 mm), from Kosa of Charlotte, N.C., U.S.A., which may be used in combination with a polyester staple fiber, for example, available from Kosa under the trade designation “T259” (3 denier, length 38 mm) and possibly also a polyethylene terephthalate (PET) fiber, for example, available from Kosa under the trade designation “T295” (15 denier, length 32 mm). Alternatively, the bicomponent fiber may comprise a generally concentric sheath-core configuration having a core of crystalline PET surrounded by a sheath of a polymer formed from isophthalate and terephthalate ester monomers. The latter polymer is heat softenable at a temperature lower than the core material. Polyester has advantages in that it can contribute to mask resiliency and can absorb less moisture than other fibers.

Alternatively, the shaping layer can be prepared without bicomponent fibers. For example, fibers of a heat-flowable polyester can be included together with staple, preferably crimped, fibers in a shaping layer so that, upon heating of the web material, the binder fibers can melt and flow to a fiber intersection point where it forms a mass, that upon cooling of the binder material, creates a bond at the intersection point. A mesh or net of polymeric strands could also be used in lieu of thermally bondable fibers. An example of this type of a structure is described in U.S. Pat. No. 4,850,347 to Skov.

When a fibrous web is used as the material for the shape-retaining shell, the web can be conveniently prepared on a “Rando Webber” air-laying machine (available from Rando Machine Corporation, Macedon, N.Y.) or a carding machine. The web can be formed from bicomponent fibers or other fibers in conventional staple lengths suitable for such equipment. To obtain a shape-retaining layer that has the required resiliency and shape-retention, the layer preferably has a basis weight of at least about 100 g/m², although lower basis weights are possible. Higher basis weights, for example, approximately 150 or more than 200 g/m², may provide greater resistance to deformation and greater resiliency. Together with these minimum basis weights, the shaping layer typically has a maximum density of about 0.2 g/cm² over the central area of the mask. Typically, the shaping layer would have a thickness of about 0.3 to 2.0, more typically about 0.4 to 0.8 millimeters. Examples of shaping layers suitable for use in the present invention are described in the following patents: U.S. Pat. No. 5,307,796 to Kronzer et al., U.S. Pat. No. 4,807,619 to Dyrud et al., and U.S. Pat. No. 4,536,440 to Berg.

The above-described method of manufacture is not intended to be limiting. At least for the region of the mask body that immediately covers nose and mouth, for example, the mask may be rigid and air-impermeable. Thus, injection molding, thermoforming, transfer- and compression molding are suitable. Even masks stamped in metal may be employed.

It is also to be understood that the foregoing descriptions are not intended to limit embodiments of the invention to any specific configuration. The ability of a particular facemask to deflect aerosols exhaled or expelled from a source may be readily determined, for example, as described below.

An in vitro bench model may be used advantageously to assess different protection strategies based on surgical masks (affecting exhalations) and respirator masks (affecting inhalations) interacting with potential exposures. FIG. 1 illustrates the principles of the model, emphasizing each measurable parameter including: the breathing patterns of the presumed infected Source and uninfected Receiver, the aerosols produced at the Source, the effects of the chamber on aerosol dilution and particle modification, the effects of filtration using filters on Source and Receiver, particle deflection by mask, and chamber air exchange. Multiple potential means of protection that masks and/or respirators may offer can be evaluated, including dilution, deflection and filtration when a mask is worn either at the source (patient) or the receiver (HCW or others).

Referring to bench model 5 in FIG. 2, one may construct an enclosure 10 that defines a chamber 20 into which radiolabeled wet aerosols simulating exhaled, particles from a subject (or “Source”) are introduced. Aerosols may be defined by cascade impaction using one or more cascade impactors 30 (Marple 8-stage impactor, Thermo Fischer Scientific, Waltham, Mass., 2 liter per minute flow), a technique well-known in the art. Source aerosols may be exhaled via a ventilated mannequin head 40 (Simulaids, Saugerties N.Y.) suitable for mask protection. A similar head 50 within the chamber may be used to assess recipient exposure (the “Receiver”). The heads may be suspended from stands 60. The head of the Source may be directed toward the Receiver or at any other angle through almost 360°. A filter 70 (Pari, Starnberg Germany) within the Receiver can be used to quantify exposure. This filter captures all inhaled particles.

The bench model 5 may be used to assess the effect of any mask 7 (or no mask) on different aspects of protection from potential exposure, including dilution, deflection and filtration, when worn either at the Source or the Receiver. Similarly, to evaluate the performance of any mask in various environments, the chamber's size and configuration and its ventilation parameters may be modified at will.

Chamber 20 may measure, for example, 135 ft³ (5 ft. in length, 5 ft. wide, 6 ft in height). The chamber is advantageously placed in the proximity of a hood suitable for exhausting radioactivity. The chamber is equipped with an air intake port and is connected to the hood via an exhaust port such that a fixed (but adjustable) exchange occurs (6 exhanges per hour, for example). Aerosols may be created by nebulizer 80 such as an AeroTech II nebulizer connected to a source of compressed air 90 with a flow, for example, of 10 L per minute. If the nebulizer 80 is filled with 3 ml of 0.9% normal saline labeled with technetium-99m and run to dryness over about 10 minutes, it will produce radiolabeled wet aerosols simulating contaminated particles exhaled during tidal breathing (Source). Each head may be connected to a pump 100 (Harvard, Millis, Mass.), set to pump a tidal volume of 500 ml, respiratory rate of 15 per minute, and duty cycle of 0.5 min. The pumps are preferably not synchronized. The heads 40 and 50 may be placed within the chamber approximately 3 feet apart. The aerodynamic distributions of expelled particles at the Source and near the Receiver may be measured by cascade impaction, as noted above (Marple 8-stage impactor, Thermo Fischer Scientific, Waltham, Mass., 2 liter per minute flow). Source aerosols may be measured by an in-line impactor 110 as shown in FIG. 3. The impactor 30, as illustrated in FIG. 2, measures particles exhaled from the Source that reach the vicinity of the Receiver. Exposure is quantified by filter 70. To avoid effects of ambient air currents, smoke tracer experiments may be performed within the chamber to assure that there are no ambient air currents. If ambient air currents are desired, they may be introduced and evaluated by smoke tracer experiments. Such experiments are conducted by providing a plume of visible aerosol particles, such as smoke rising from the tip of a lit cigarette, and plotting its motion vectors.

The experimental design outlined above is organized to assess factors likely important in exposure, dilution, deflection and filtration of defined aerosols. The chamber and mannequin head set-up are constructed (CDC recommended distance of 3 feet apart[5]) to mimic two individuals sitting in a room representing a typical environment. The choice of a tidal breathing pattern best represents the most common clinical interaction between two persons. The choice of aerosols reflects the characteristics of wet aerosols that are exhaled by humans during tidal breathing [14, 15].

Dilution

To test particular mask designs, one may first perform experiments with heads 40 and 50 facing directly towards each other with no masks worn either at the Source or the Receiver. Maximum exposure (Max Ex) is quantified as the percent of nebulized particles captured (i.e. inhaled) by the Receiver and is a direct reflection of dilution of exhaled particles by mixing with ambient air.

Deflection & Filtration on Source

Different surgical mask and respirator configurations placed on the Source assess the combined effects of filtration (defined as aerosol captured by the mask) and deflection (particles not captured by filtration and deflected away from the Receiver). Pure filtration of Source aerosols may be measured by sealing the respirator to the face with Vaseline and insuring that environmental flow in the chamber is zero

Filtration and Fit

The same mask configurations can be tested on the Receiver to measure effects of aerosols modified by the chamber environment and reaching the vicinity of the Receiver. This approach assesses both filtration protection and effects of fit, i.e. aerosol leaking between mask and smooth face vs. perfect seal (Vaseline).

Perfect seal is defined by a bead of Vaseline placed around the perimeter of the respirator on both the Source and Receiver (the surgical masks were not sealed to the face).

Measurements and Data

Experiments may be run for a total of 10 minutes (nebulizer to dryness). Radioactivity captured by either the exposure filter (at Receiver) or mask (at Source or Receiver) may be measured with a calibrated well counter (≦10 Kemble Instruments, Hamden, Conn.) or a calibrated Ratemeter (>10 Ludlum Measurements Inc., Sweetwater Tx). Data may be presented as percent of nebulized particles and expressed as mean+/−confidence intervals. Separation of confidence intervals define statistical significance. The ratio of Max Ex to actual exposure defines a Workplace Protection Factor (WPF, NIOSH) [16].

The goal of mask protection is to reduce exposure to the Receiver independent of environmental engineering control systems. At least for aerosols generated under conditions comparable to those experienced in the HCW environment, manipulating the Source rather than trying to simply protect the Receiver is highly advantageous, becoming optimal when a mask is sealed to the sides of the Source's face and has vents cephalad and caudad (FIGS. 4, 5). When sealed to the Receiver, by contrast, particles passed through the mask and are inhaled.

EXPERIMENTAL

These examples present representative protocols used in describing the invention disclosed herein. These protocols are not to be considered limiting as any analogous or comparable protocol measuring the same end-points within the skill of an ordinary artisan would also be sufficient.

An in vitro bench model was designed to assess the effect of surgical mask and respirator interaction on different mechanisms of protection from potential exposure. FIG. 1 illustrates the principles of the model emphasizing each measurable parameter including: the breathing patterns of the presumed infected Source and uninfected Receiver, the aerosols produced at the Source, the effects of the chamber on aerosol dilution and particle modification, the effects of filtration using filters on Source and Receiver, particle deflection by mask, and chamber air exchange. Multiple potential mechanisms of protection that masks and/or respirators may offer, including dilution, deflection and filtration when worn either at the source (patient) or the receiver (HCW or others) were examined. The goal was to provide a scientific basis for designing future clinical studies.

Methods: Experimental Setup

FIG. 2 is a schematic representation of the experimental setup. To quantify exposure, a chamber measuring 135 ft³ (5 ftl×4.5 ftw×6 fth) was constructed. The chamber was placed next to a hood with a small connection providing a fixed, defined flow providing 6 air exchanges/hr. Aerosols were created by an AeroTech II nebulizer (3 devices used in rotation, Biodex, Shirley, N.Y.) connected to an air tank with a flow of 10 L per minute. The nebulizer was filled with 3 ml of 0.9% normal saline labeled with technetium-99m and run to dryness over about 10 minutes. It produced radiolabeled wet aerosols simulating contaminated particles exhaled during tidal breathing (Source). Source aerosols were exhaled via a ventilated mannequin head (“Brad” Model #2512, Simulaids, Saugerties N.Y.) suitable for mask protection and directed towards the Receiver. A similar ventilated head was placed within the chamber to assess recipient exposure (Receiver). Each head was connected to a Harvard pump (Harvard Apparatus SN#A52587, Millis, Mass.), tidal volume 500 ml, respiratory rate of 15, and duty cycle of 0.5. The ventilators were not synchronized. The heads were placed within the chamber approximately 3 feet apart. In separate experiments the aerodynamic distributions of expelled particles at the Source and near the Receiver were measured in triplicate by cascade impaction (Marple 8-stage impactor, Thermo Fischer Scientific, Waltham, Mass., 2 liter per minute flow). Source aerosols were measured as shown in FIG. 3. The impactor, as illustrated in FIG. 2, also measured particles exhaled from the Source reaching the vicinity of the Receiver. Aerosols near the Receiver were measured with and without masks placed on the Source. Exposure was quantified by placing a filter (Pari, Starnberg Germany) within the Receiver head, which captured all inhaled particles. two types of masks were tested, a NIOSH approved N95 respirator (Model#18605, 3M, St. Paul, Minn.) and an ear loop surgical mask (Model #GCFCXS, Crosstex International Inc., Hauppauge, N.Y.). Several mask combinations were assessed: no mask, a surgical mask tightly fit on the Source (STSM), a surgical mask loosely fit on the Source (SLSM), a surgical mask loosely fit on the Receiver (RLSM), a surgical mask tightly fit on the Receiver (RTSM), an N95 on the Source (SN95) and an N95 on the Receiver (RN95). N95 masks were sized to fit the mannequin with no visible or otherwise obvious leaks. To further maximize fit, additional experiments were performed with the N95 sealed to the face with Vaseline (soap bubble tested, RN95Vas, SN95Vas) to prevent leaks. Smoke tracer experiments were performed within the chamber defining ambient air currents. Using a calibrated LoFlo balometer (Model #6200, Alnor, Huntington Beach, Calif.), chamber flow towards the hood was usually either 14 ft³/min or 0 ft³/min. A limited number of measurements were made at a higher environmental flow rate of 20 ft³/min. (Results in Table 2). Relative humidity and temperature ranged from 21%-26% and 20-22° C. respectively.

The experimental design was organized to assess factors likely important in exposure, dilution, deflection and filtration of defined aerosols. The chamber and mannequin head set-up were constructed (CDC recommended distance of 3 feet apart [5]) to mimic two individuals sitting in a room representing a typical environment. A tidal breathing pattern was chosen in order to best represent the most common clinical interaction between two persons. Aerosols were chosen based upon the characteristics of wet aerosols that are exhaled by humans during tidal breathing [14, 15].

Dilution

The first series of experiments were performed with the heads facing directly towards each other with no masks worn either at the Source or the Receiver. Maximum exposure (Max Ex) was quantified as the percent of nebulized particles captured (i.e. inhaled) by the Receiver and is a direct reflection of dilution, of exhaled “infectious particles” by mixing with ambient air.

Deflection & Filtration on Source

Different surgical mask and respirator configurations placed on the Source assessed the combined effects of filtration (defined as aerosol captured by the mask) and deflection (particles not captured by filtration and deflected away from the Receiver). Pure filtration of Source aerosols was measured by sealing the respirator to the face with Vaseline and insuring that environmental flow in the chamber was 0. Deflection was further investigated by rotating the Source 90 degrees (e g turning Source head to left).

Filtration and Fit

The same mask configurations were tested on the Receiver, which measured effects of aerosols modified by the chamber environment and reaching the vicinity of the Receiver. This approach assessed both filtration protection and effects of fit i.e. aerosol leaking between mask and smooth face vs. perfect seal (Vaseline).

Perfect seal was defined by a bead of Vaseline placed around the perimeter of the respirator on both the Source and Receiver and leak tested with liquid soap (the surgical masks were not sealed to the face).

“Open” Masks on Source

FIG. 5 and FIG. 6 illustrate a mask design according to an embodiment of the invention. The Model #GCFCXS, Crosstex N95 mask, which is equipped with metal stays to ensure tight closure over the nose-bridge and chin was modified by bending the stays to ensure that the edges of the mask would remain spaced apart from the nose-bridge and the chin. In one case, the modified mask was further modified to ensure that the lateral edges remained spaced apart from the cheeks.

Measurements and Data

All experiments were run for a total of 10 minutes (nebulizer to dryness). Radioactivity that was captured by either the exposure filter (at Receiver) or mask (at Source or Receiver) was measured with a calibrated well counter (≦10 μCi, Kemble Instruments, Hamden, Conn.) or a calibrated Ratemeter (>10 μCi, Ludlum Measurements Inc., Sweetwater Tx). Data were presented as percent of nebulized particles and expressed as mean+/−confidence intervals. Separation of confidence intervals defined statistical significance. The ratio of Max Ex to actual exposure defined a simulated Workplace Protection Factor (sWPF, NIOSH) [16].

Results: Aerosol Particle Distribution

Complete particle distributions and Mass Median Aerodynamic Diameters (MMAD) are summarized in FIG. 4. Data are plotted as log aerodynamic diameter vs. probability with confidence intervals. Particles leaving the Source were similar to exhaled droplets in vivo as approximately 95% of the particles were less than 2 μm, with an average MMAD of 1.046 μm (95% CI 0.984-1.11) [14, 15]. Particles in the vicinity of the Receiver when no masks were worn were significantly smaller; most (75%) were sub-micronic with an average MMAD of 0.633 μm (95% CI 0.511-0.756). Masks placed on the Source further decreased particle size near the Receiver with approximately 85% sub-micronic and an average MMAD of 0.483 μm (95% CI 0.408-0.558), 0.461 μm (95% CI 0.450-0.47), and 0.470 μm (95% CI 0.290-0.650) when the LSM, TSM and N-95 masks were placed on the Source respectively.

Exposure; Source Manipulation vs. Receiver Manipulation (% of Nebulized Particles)

Exposure to the Receiver and the corresponding sWPF are shown in Table 1 (left panel). Data are separated by process and reported as percentage of nebulized particles. The quantified effects of each maneuver on exposure are best illustrated in the sWPF. Max Ex averaged 1.09% (95% CI 0.902-1.29) indicating the effect of dilution (i.e. from 100%). Applying either a surgical mask or N95 respirator at the source resulted in significant reductions in exposure and corresponding sWPFs of 260-350.

Applying either surgical mask or respirator to the Receiver (without a perfect seal) did not significantly reduce exposure from that of no masks (sWPF of 1.38-3.18).

Mask Filtration (% of Nebulized Particles)

Radioactivity captured by each mask quantified the effectiveness of filtration on exposure. At the Source, SN95 resulted in significantly greater filtration averaging 35.7% (95% CI 27.7-43.7) in comparison to STSM 13.4% (95% CI 10.8-16.1) and SLSM 5.98% (95% CI 5.22-6.74). However, significantly greater filtration did not result in a significant reduction in exposure indicating deflection was the dominant factor.

Filtration at the Receiver offered no significant protection capturing an average of 0.0856% (95% CI −0.00564-0.177), 0.108% (95% CI 0.591-0.156) and 0.135% (95% CI 0.0641-0.206) when the RLSM, RTSM and RN95 were applied respectively. Statistically, the N95 respirator provided no extra benefit over the surgical masks.

Sealing the N95 to the face demonstrated the importance of fit. The sealed N95 respirator (SN95Vas) was representative of filtration combined with deflection at the Source which provided the best protection overall in terms of sWPF (4104). Filtration captured a mean of 81.0% (95% CI 59.5-102) of the particles. When placed on the Receiver (RN95Vas) the protective value diminished to a sWPF of 119 capturing an average of 0.453% (95% CI −0.020-0.926).

Deflection at the Source

When the Source head was rotated (SLSM 90, STSM 90, SN95 90) sWPF decreased from 260 to 5.99, 290 to 129 and 350 to 15.1 respectively. Although exposure at the receiver was increased, masks on the Source still significantly reduced exposure particularly the tight surgical mask, further demonstrating the potential contribution of deflection in reducing exposure.

Mask Combination

Masks on both the Source and Receiver appeared protective compared to “no masks”. However, protection was not at the same level as Source protection alone (sWPF 88-181 vs. 260-350). These trends, while not significant, were suggestive of other factors in aerosol transmission from Source to Receiver. (See discussion)

Absence of Deflection

For these experiments the communication with the hood was sealed at the piston ventilator connection to the Source. This essentially eliminated all air circulation in the chamber except for the ventilated and nebulized gases. These Data are listed in Table 1 (right panel).

Maximum exposure was similar to that measured during environmental flow with approximately 1% of the aerosol reaching the Receiver. Without environmental flow, sWPF for all mask combinations were not significantly increased beyond Max Exposure (e.g. sWPF ranging from 1 to 4) indicating that particles simply filled the space and masks did not reduce exposure. The only exceptions were the sealed respirator experiments. SN95Vas and RN95Vas resulted in sWPF of 16 and 101 respectively. Of note there was a marked difference between the sWPF SN95Vas with environmental flow vs no flow (4082 vs 16).

Mask with Open Edges

Table 3 (statistical details in Table 4) compares a conventionally fitted mask to two “open” modifications of the same mask. Opening the mask's plenum cephalad and caudad improves WPF by almost an order of magnitude over that provided by a mask that relies solely on filtration. The entire gain is lost when the mask is additionally opened laterally.

Discussion:

The goal of mask protection is to reduce exposure to the Receiver independent of environmental engineering control systems presumably by filtration. The data shown herein, however, indicate that mask protection can be more effective than that provided only by filtration if the interaction between mask deflection of particles and environmental airflow is utilized. For exhaled particles, this study demonstrates the value of manipulating the Source rather than trying to simply protect the Receiver. The most important factor in reducing exposure was deflection of exhaled particles at the Source. This process required some movement of air in the space comparable to the flows routinely found in public environments (6 air exchanges per hour).

Aerosols generated were comparable to those experienced in the HCW environment. It was observed that wet aerosols emitted from a potentially infectious Source evaporate to sub-micron particles capable of penetrating the N95 respirator. The model disclosed herein consistently demonstrated that containing exhaled particles at the Source resulted in greater protection to the Receiver. Mask filtration with a respirator appeared effective only when physically sealed to the Source's face.

Dilution alone reduced exposure to the Receiver 100-fold (WPF≈1). Placing a surgical mask on the Source further decreased exposure by an additional 275-fold (WPF≈275). In comparison, sealing an N95 respirator on the Receiver provided less protection (WPF≈100 and if unsealed, no protection (WPF≈1). Deflection and dilution appear to be the dominant factors affecting aerosol transmission. In the model examined herein, filtration protection at the Receiver appears to play a minor role. The importance of deflection was further illustrated when the Source head was rotated, as a tightly fitted surgical mask was the best “deflector”.

For deflection to be effective the deflected particles must be carried away. In the absence of environmental flow, the space fills with particles and masks are not effective unless perfectly sealed to the face. With filtration as the only mechanism of protection (SN95Vas and RN95Vas) sWPF ranged from 16 to 101. The superior level of protection at the Source seen with environmental flow using a sealed respirator (SN95Vas) with a sWPF of 4000 was due to a combination of filtration and deflection, dropping to a sWPF of 16 when deflection was eliminated (environmental flow of 0).

Numerous studies have focused only on filtration efficiency of both N95 respirators and surgical masks placed on the Receiver [8-11, 17]. The CDC currently recommends HCWs wear N95 respirators for protection against certain pathogens that may be transmitted via aerosol. On the bench, NIOSH requires that N95 respirators filter 95% of a test aerosol of 0.3 μm particles [10, 18]. In the present examples, aerosols measured near the receiver, (0.5 μm or smaller) overlap in distribution with potentially infectious viral particles [10, 19].

The study summarized herein, as well as previous studies, point to the importance of fit [9, 18, 20]. Unfortunately, fit-testing has serious limitations. Coffey et al. tested 25 humans with 21 different models of N95 respirators. Only 4 of the 21 masks successfully fit more than 50% of the subjects [21]. A second study by the same group reported similar findings when 18 models of N95 were tested with five different fit-test methods [22]. They also described significant variability among the different fit-test methods and pointed out that simply passing a qualitative fit-test did not necessarily guarantee the wearer an adequately fitting respirator.

Conclusions

Mask filtration, applied either at the Source or the Receiver, does not play a significant role in reducing exposure to the recipient unless a respirator is physically sealed to the face of the Source. Deflection of exhaled particles, such as can be achieved with a surgical mask worn at the Source, achieves far greater levels of protection than an N95 respirator on the recipient, provided that there is some degree of airflow in the enclosure that Source and Receiver occupy. Thus, for example, a nurse in a one on one situation with a patient may optimally reduce his/her exposure by placing a surgical mask on the patient after insuring that there is some degree of airflow in the room. This situation also maximizes HCW compliance because the HCW does not need to wear a mask. If airflow is ‘still’ with no perceived ventilation then the HCW may expect only a minimal degree of protection from any mask. The HCW worker is further protected if the Source is wearing a mask that properly contacting the cheeks laterally and has a plenum that is open communication above and below with the environment.

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I claim:
 1. A facemask configured to be worn by a subject, said facemask comprising an air-permeable body having, when worn, an outer surface facing away from the face of said subject, an inner surface facing toward said face, an upper edge cephalad, a lower edge caudad, and lateral edges at each side of said face such that: a) said inner surface covers said nose and mouth and is spaced apart therefrom so as to create a plenum defined by said upper, lower and lateral edges and having only first and second openings; b) at least a portion of said upper edge is spaced apart from said face so as to define said first opening; c) at least a portion of said lower edge is spaced apart from said face so as to define said second opening, and d) said lateral edges are not spaced apart from said face and contact the cheeks of said face.
 2. The facemask of claim 1, wherein said plenum extends cephalad to said first opening.
 3. The facemask of claim 1, wherein said plenum extends caudad to said second opening.
 4. The facemask of claim 1, wherein said body comprises a rigid material.
 5. The facemask of claim 1, wherein said body comprises a flexible material.
 6. The facemask of claim 5, wherein said flexible material is elastic.
 7. The facemask of claim 1, wherein said body comprises a first portion comprising an air-impermeable material and a second portion comprising an air-permeable material.
 8. A system comprising: a) a facemask according to claim 1, and b) an enclosure comprising a floor, a ceiling and a wall therebetween, wherein said floor, ceiling and wall define an enclosed space, and wherein said enclosed space contains an ambient, breathable gas.
 9. The system of claim 9, wherein said enclosed space comprises an overhead space, a mid-level space disposed below said overhead space, and a lower-level space disposed below said mid-level space, wherein said overhead and mid-level spaces are contiguous and in fluid communication and wherein said mid-level and lower-level spaces are contiguous and in fluid communication.
 10. The system of claim 9, wherein said enclosure is ventilated.
 11. The system of claim 10, wherein said ceiling, wall or floor is fenestrated.
 12. The system of claim 10, wherein said enclosure is ventilated at a rate of at least five enclosure volume exchanges per hour.
 13. The system of claim 10, wherein said enclosure is ventilated by an air handler.
 14. A method of positioning a facemask on a human subject, comprising a) providing a facemask comprising an air-permeable body having an outer surface, an inner surface, an upper edge, a lower edge and lateral edges; and b) positioning said facemask on the face of said human subject such that said outer surface faces away from the face of said subject, said inner surface faces toward said face, said upper edge is positioned cephalad, said lower edge is positioned caudad, and said lateral edges contact each side of said face such that: i) said inner surface covers the human subject's nose and mouth and is spaced apart therefrom so as to create a plenum defined by said upper, lower and lateral edges and having only first and second openings; ii) at least a portion of said upper edge is spaced apart from said face so as to define said first opening; v) at least a portion of said lower edge is spaced apart from said face so as to define said second opening, and vi) said lateral edges are not spaced apart from said face and are in contact with the cheeks of said face.
 15. A method of reducing an accumulation of aerosol particles in at least a mid-level space of a ventilated enclosure consequent to an aerosol plume created by a subject in said enclosure, the method comprising: a) providing i) said subject; ii) said ventilated enclosure; iii) a facemask according to claim 1, iv) a pre-determined standard accumulation of said airborne aerosol particles in said mid-level space; b) positioning said facemask according to the method of claim 14 on said face over said nose and mouth to create a positioned mask, and c) causing said subject to create an aerosol plume, such that said accumulation is less than said standard accumulation.
 16. The method of claim 29, wherein said subject has, or is suspected of having, a disease spread by airborne aerosol particles. 